Low cost phased array antennae are required on naval ships, land-based radar stations and similar areas. Traditional phased array antennae using periodic lattices and transmit/receive modules are prohibitive in cost. When an antenna is designed for use with short wavelengths, the transmit/receive modules are bulky and cannot be positioned between antenna elements. Also, advanced radar designs require low sidelobe architecture, and in some instances, many subarrays are desired.
One prior art approach uses a traditional periodic array orientation of subarrays. It has been found that this type of prior art phased array antenna produces grating lobes. This is especially true at higher frequency applications, such as the X-band and Ku-band. Even lower frequency applications than the UHF, L-band and S-band have been found to produce grating lobes.
Commonly assigned U.S. Pat. No. 6,456,244, the disclosure which is hereby incorporated by reference in its entirety, discloses a phased array antenna that includes a plurality of subarray lattices arranged in an aperiodic array lattice. Each subarray lattice includes a plurality of antenna elements arranged in an aperiodic configuration on a multilayer circuit board. Typically, the elements are arranged in a spiral configuration. This type of arrangement is a low-cost approach for reducing sidelobes and grating lobes. In one aspect, it is similar to other periodic and aperiodic arrays that are typically designed with a circular or square overall aperture shape. Some phased array antenna have been designed with a periodic triangular grid and circular aperture with a nominal 8×8 degree symmetrical beam.
This type of phased array antenna as described is not as advantageous if a transmit beam with a different aspect ratio is required, such as greater in azimuth than elevation. For example, a phased array antenna could require the same width, but three or four times the height. This could be accomplished by increasing the number of elements by 4:1. This would cut the power for each element by 4:1, however, and the resulting array costs would increase by at least 3:1, increasing the cost, size and weight of the overall phased array antenna. Periodic arrays are typically forced to this configuration in conventional designs because the element spacing is limited to nearly one-half wavelength. It would be advantageous if aperiodic grid techniques could be used to solve these problems.